Gamma correction for distance field text.

Handles both non-LCD and LCD text. Uses a texture to look up the gamma correction values for a given text color or luminance.

BUG=skia:
R=reed@google.com, bungeman@google.com, robertphillips@google.com, bsalomon@google.com

Author: jvanverth@google.com

Review URL: https://codereview.chromium.org/258883002

1 files changed, 34 insertions, 8 deletions

diff --git a/src/core/SkPaint.cpp b/src/core/SkPaint.cpp
index 78d947020b..b08b2c6da7 100644
--- a/src/core/SkPaint.cpp
+++ b/src/core/SkPaint.cpp
@@ -1814,10 +1814,8 @@ void SkScalerContext::PostMakeRec(const SkPaint&, SkScalerContext::Rec* rec) {
 
 /*
  *  ignoreGamma tells us that the caller just wants metrics that are unaffected
- *  by gamma correction, so we jam the luminance field to 0 (most common value
- *  for black text) in hopes that we get a cache hit easier. A better solution
- *  would be for the fontcache lookup to know to ignore the luminance field
- *  entirely, but not sure how to do that and keep it fast.
+ *  by gamma correction, so we set the rec to ignore preblend: i.e. gamma = 1,
+ *  contrast = 0, luminanceColor = transparent black.
  */
 void SkPaint::descriptorProc(const SkDeviceProperties* deviceProperties,
                              const SkMatrix* deviceMatrix,
@@ -1827,7 +1825,7 @@ void SkPaint::descriptorProc(const SkDeviceProperties* deviceProperties,
 
     SkScalerContext::MakeRec(*this, deviceProperties, deviceMatrix, &rec);
     if (ignoreGamma) {
-        rec.setLuminanceColor(0);
+        rec.ignorePreBlend();
     }
 
     size_t          descSize = sizeof(rec);
@@ -1951,9 +1949,10 @@ void SkPaint::descriptorProc(const SkDeviceProperties* deviceProperties,
 }
 
 SkGlyphCache* SkPaint::detachCache(const SkDeviceProperties* deviceProperties,
-                                   const SkMatrix* deviceMatrix) const {
+                                   const SkMatrix* deviceMatrix,
+                                   bool ignoreGamma) const {
     SkGlyphCache* cache;
-    this->descriptorProc(deviceProperties, deviceMatrix, DetachDescProc, &cache, false);
+    this->descriptorProc(deviceProperties, deviceMatrix, DetachDescProc, &cache, ignoreGamma);
     return cache;
 }
 
@@ -1969,6 +1968,33 @@ SkMaskGamma::PreBlend SkScalerContext::GetMaskPreBlend(const SkScalerContext::Re
     return maskGamma.preBlend(rec.getLuminanceColor());
 }
 
+size_t SkScalerContext::GetGammaLUTSize(SkScalar contrast, SkScalar paintGamma,
+                                        SkScalar deviceGamma, int* width, int* height) {
+    SkAutoMutexAcquire ama(gMaskGammaCacheMutex);
+    const SkMaskGamma& maskGamma = cachedMaskGamma(contrast,
+                                                   paintGamma,
+                                                   deviceGamma);
+
+    maskGamma.getGammaTableDimensions(width, height);
+    size_t size = (*width)*(*height)*sizeof(uint8_t);
+
+    return size;
+}
+
+void SkScalerContext::GetGammaLUTData(SkScalar contrast, SkScalar paintGamma, SkScalar deviceGamma,
+                                      void* data) {
+    SkAutoMutexAcquire ama(gMaskGammaCacheMutex);
+    const SkMaskGamma& maskGamma = cachedMaskGamma(contrast,
+                                                   paintGamma,
+                                                   deviceGamma);
+    int width, height;
+    maskGamma.getGammaTableDimensions(&width, &height);
+    size_t size = width*height*sizeof(uint8_t);
+    const uint8_t* gammaTables = maskGamma.getGammaTables();
+    memcpy(data, gammaTables, size);
+}
+
+
 ///////////////////////////////////////////////////////////////////////////////
 
 #include "SkStream.h"
@@ -2557,7 +2583,7 @@ SkTextToPathIter::SkTextToPathIter( const char text[], size_t length,
         fPaint.setPathEffect(NULL);
     }
 
-    fCache = fPaint.detachCache(NULL, NULL);
+    fCache = fPaint.detachCache(NULL, NULL, false);
 
     SkPaint::Style  style = SkPaint::kFill_Style;
     SkPathEffect*   pe = NULL;